Carl Zimmer presents a timeline of the Homo floresiensis story, with a summary of the latest paper that casts doubt on its status as a legitimate species. Bottom line: it’s still unsettled! As usual, the answer is only going to come from more digging and more data on the populations that lived on Ling Bua.
Sometimes a plan just comes together beautifully. I’m flying off to London tomorrow, and on the day I get back to Morris, I’m supposed to lead a class discussion on the final chapters of this book we’ve been reading, Endless Forms Most Beautiful. I will at that point have a skull full of jet-lagged, exhausted mush, and I just know it’s going to be a painful struggle. Now into my lap falls a wonderful gift.
There was a review in the NY Review of Books that said wonderful things about Carroll’s work, and in particular about the revolutionary nature of evo-devo. This prompted Jason Hodin, an evo-devo researcher himself (whose work I’ve mentioned before) to write a rebuttal and send it off to NYRB…which they chose not to publish. So he sent it to me, with permission to post it.
(If Pharyngula is going to be second choice to the NY Review of Books, I’m not going to complain.)
Anyway, I’m almost as guilty as Carroll of hawking the wares of the evo-devo bandwagon and traveling roadshow, so this is a welcome balancing corrective. The complete text is below the fold.
How we sense the world has, ultimately, a cellular and molecular basis. We have these big brains that do amazingly sophisticated processing to interpret the flood of sensory information pouring in through our eyes, our skin, our ears, our noses…but when it gets right down to it, the proximate cause is the arrival of some chemical or mechanical or energetic stimulus at a cell, which then transforms the impact of the external world into ionic and electrical and chemical changes. This is a process called sensory signaling, or sensory signal transduction.
While we have multiple sensory modalities, with thousands of different specificities, many of them have a common core. We detect both light and odor (and our cells also sense neurotransmitters) with similar proteins: they use a family of G-protein-linked receptors. What that means is that the sensory stimulus is received by a receptor molecule specific for that stimulus, which then actives a G-protein on the intracellular side of the cell membrane, which in turn activates an effector enzyme that modifies the concentration of second messenger molecules in the cell. Receptors vary—you have a different receptor for each molecule you can smell. The effector enzymes vary—it can be adenylate cyclase, which changes the levels of cyclic AMP, or it can be phospholipase C, which generates other signalling molecules, DAG and IP3. The G-protein that links receptor and effector is the common element that unites a whole battery of senses. The evolutionary roots of our ability to see light and taste sugar are all tied together.
Nick Matzke has
compiled all the data on hominin cranial capacities into a single chart:
I think I can see a pattern there, can you? He also has data on body size and brain size over there, take a gander at it. It looks like a simple and obvious example of evolutionary change in our lineage, I think.
Alas, it only shows specimens older than 10,000 years. I’m sure that right around 6,000 years ago, there was a sudden, dramatic change as the deity injected a soul into those crania.
Here’s a prediction for you: the image below is going to appear in a lot of textbooks in the near future.
That’s a technical tour-de-force: it’s a confocal image of a Drosophila embryo, stained with 7 fluorescent probes against different Hox genes. You can clearly see how they are laid out in order from the head end (at the left) to the tail end (which extends to the right, and then jackknifes over the top). Canonically, that order of expression along the body axis corresponds to the order of the genes in a cluster on the DNA, a property called colinearity. I’ve recently described work that shows that, in some organisms, colinearity breaks down. That colinearity seems to be a consequence of a primitive pattern of regulation that coupled the timing of development to the spatial arrangements of the tissues, and many organisms have evolved more sophisticated control of these patterning genes, making the old regulators obsolete…and allowing the clusters to break up without extreme consequences to the animal. A new review in Science by Lemons and McGinnis that surveys Hox gene clusters in different lineages shows that the control of the Hox genes is much, much more complicated than previously thought.
Carl Zimmer brings up another essential point about the HAR1F study: it was work that was guided by evolutionary theory. The sequence would not have been recognized in the billions of nucleotides in the genome if it hadn’t been for an analysis directed by the principles of evolution.
Wells’ diatribe was amazingly wrong. I looked at it again and there could be another half-dozen essays in just picking up apart the stupidity in it.
There are days when I simply cannot believe how dishonest the scoundrels at the Discovery Institute can be. This is one of them. I just read an essay by Jonathan Wells that is an appalling piece of anti-scientific propaganda, an extremely squirrely twisting of some science news. It’s called “Why Darwinism is doomed”, and trust me, if you read it, your opinion of Wells will drop another notch. And here you thought it was already in the gutter!
It’s April (not anymore—it’s September as I repost this), it’s Minnesota, and it’s snowing here (not yet, but soon enough). On days like this (who am I fooling? Every day!), my thoughts turn to spicy, garlicky delicacies and warm, sunny days on a lovely tropical reef—it’s a squiddy day, in other words, and I’ve got a double-dose of squidblogging on this Friday afternoon, with one article on the vampire squid, Vampyroteuthis infernalis, and this one, on squid evolution and cephalopod Hox genes.
Archy goes looking for mastodons, finds fanged hippos with massive organs instead.
We need to appreciate beer more. Alcohol has a long history in human affairs, and has been important in purifying and preserving food and drink, and in making our parties livelier. We owe it all to a tiny little microorganism, Saccharomyces cerevisiae, which converts complex plant sugars into smaller, simpler, more socially potent molecules of ethanol. This is a remarkable process that seems to be entirely to our benefit (it has even been argued that beer is proof of the existence of God*), but recent research has shown that the little buggers do it all entirely for their own selfish reasons, and they’ve been busily making alcohol that has gone undrunk by humankind for tens of millions of years.
